Update go1.21 and CI (#315)

* Update to go 1.21

Use `atomic.Bool` stdlib instead of including our own.

Include `tools\mkwinsyscall` updates from go-winio/283 to switch to
`syscallN`.
Note: removed `// TODO` about `print`/`ln`, since the latter adds spaces
between args when printing, which is undesired.

Also update CI to run steps on windows-2022 instead of windows-2019,
similar to our hcsshim CI.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

* PR: simplify type checking

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

---------

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

tools/mkwinsyscall/mkwinsyscall.go

@@ -21,7 +21,6 @@ import (
 	"path/filepath"
 	"runtime"
 	"sort"
-	"strconv"
 	"strings"
 	"text/template"
 
@@ -541,53 +540,17 @@ func (f *Fn) ParamPrintList() string {
 	return join(f.Params, func(p *Param) string { return fmt.Sprintf(`"%s=", %s, `, p.Name, p.Name) }, `", ", `)
 }
 
-// ParamCount return number of syscall parameters for function f.
-func (f *Fn) ParamCount() int {
-	n := 0
-	for _, p := range f.Params {
-		n += len(p.SyscallArgList())
-	}
-	return n
-}
-
-// SyscallParamCount determines which version of Syscall/Syscall6/Syscall9/...
-// to use. It returns parameter count for correspondent SyscallX function.
-func (f *Fn) SyscallParamCount() int {
-	n := f.ParamCount()
-	switch {
-	case n <= 3:
-		return 3
-	case n <= 6:
-		return 6
-	case n <= 9:
-		return 9
-	case n <= 12:
-		return 12
-	case n <= 15:
-		return 15
-	default:
-		panic("too many arguments to system call")
-	}
-}
-
 // Syscall determines which SyscallX function to use for function f.
 func (f *Fn) Syscall() string {
-	c := f.SyscallParamCount()
-	if c == 3 {
-		return syscalldot() + "Syscall"
-	}
-	return syscalldot() + "Syscall" + strconv.Itoa(c)
+	return syscalldot() + "SyscallN"
 }
 
-// SyscallParamList returns source code for SyscallX parameters for function f.
+// SyscallParamList returns source code for SyscallN parameters for function f.
 func (f *Fn) SyscallParamList() string {
-	a := make([]string, 0)
+	a := make([]string, 0, len(f.Params))
 	for _, p := range f.Params {
 		a = append(a, p.SyscallArgList()...)
 	}
-	for len(a) < f.SyscallParamCount() {
-		a = append(a, "0")
-	}
 	return strings.Join(a, ", ")
 }
 
@@ -962,8 +925,6 @@ func main() {
 	}
 }
 
-// TODO: use println instead to print in the following template
-
 const srcTemplate = `
 {{define "main"}} //go:build windows
 
@@ -1001,9 +962,11 @@ func errnoErr(e {{syscalldot}}Errno) error {
 	case errnoERROR_IO_PENDING:
 		return errERROR_IO_PENDING
 	}
-	// TODO: add more here, after collecting data on the common
-	// error values see on Windows. (perhaps when running
-	// all.bat?)
+	{{- /*
+	TODO: add more here, after collecting data on the common
+	error values see on Windows. (perhaps when running
+	all.bat?
+	*/}}
 	return e
 }
 
@@ -1045,7 +1008,7 @@ func {{.HelperName}}({{.HelperParamList}}) {{template "results" .}}{
 
 {{define "results"}}{{if .Rets.List}}{{.Rets.List}} {{end}}{{end}}
 
-{{define "syscall"}}{{.Rets.SetReturnValuesCode}}{{.Syscall}}(proc{{.DLLFuncName}}.Addr(), {{.ParamCount}}, {{.SyscallParamList}}){{end}}
+{{define "syscall"}}{{.Rets.SetReturnValuesCode}}{{.Syscall}}(proc{{.DLLFuncName}}.Addr(), {{.SyscallParamList}}){{end}}
 
 {{define "tmpvarsreadback"}}{{range .Params}}{{if .TmpVarReadbackCode}}
 {{.TmpVarReadbackCode}}{{end}}{{end}}{{end}}